1. Field of the Invention
The present invention relates to a fuel injection control apparatus for an engine, and more particularly, to a fuel injection control apparatus for a small outboard engine that is started by manual rotation of a crank shaft.
2. Description of the Related Art
In a small outboard engine with small displacement, fuel supply by a carburetor system is mainly used. A battery or the like is not equipped therein. For the start of the small outboard engine, a recoil starting device is equipped rather than a starter or the like and an operator manually starts the small outboard engine. In this manner, in general, the small outboard engine is light in weight and low in cost.
In recent years, fuel supply for the small outboard engine with small displacement is changed from one based on the carburetor system to an electronic control system for the purpose of improvement of operability, maintainability, exhaust gas purification, and output performance. However, in order that an engine be configured to be small in size, light in weight, and low in cost, a starting device such as a starter, a battery, and the like are often not mounted therein. There is an apparatus including an injector and a fuel pump that perform fuel supply to an engine, a fuel pressure regulator that keeps fuel pressure constant, a sensor that detects operation state of the engine, and an electronic control unit (ECU) as control means for performing fuel control. The apparatus is equipped with a generator that performs power supply to those devices. The apparatus actuates the ECU and the injector based on a power supply of the generator upon driving of the engine and is not mounted with a battery (see, for example, Japanese Patent No. 3858582 B).
There is also an apparatus that improves startability by switching the use of an electric fuel pump that supplies fuel using an output of a generator according to manual start and a mechanically-driven fuel pump that receives mechanical driving force and supplies fuel according to manual start (see, for example, Japanese Patent Application Laid-Open No. 2005-330815).
When the engine is started, in particular, in the fuel control apparatus not equipped with a battery, the injector, the electric fuel pump, and the ECU cannot be started and the fuel supply cannot be performed unless the generator that performs generation with driving force from the crank shaft of the engine sufficiently generates power. Therefore, during manual start operation, first, power is generated by cranking. Then, the device such as the ECU is started. After the ECU is started, the ECU calculates a fuel supply amount based on a state of the engine, fuel supply to the engine is started by injector driving, engine torque is generated by combustion through an ignition after that, and the operation of the engine itself is started.
Before calculating injector driving time in the ECU in order to supply the fuel to the engine during the engine start and driving the injector for the calculated period of time, it is necessary to drive the electric fuel pump, raise the pressure of the fuel supplied to the injector, and keep the pressure at a predetermined value. Even if the injector is driven for the same period of time, a fuel amount supplied to the engine is different if the fuel pressure is different. Therefore, in some case, when a fuel amount necessary for starting the engine is smaller than a requested value, the combustion through the ignition is unstable. Unlike the start by the starter or the like, in manual cranking, the cranking can be continued only for several rotations of the engine. Therefore, in some case, the engine itself cannot be started.
Therefore, it is necessary to start power generation as early as possible during the manual cranking, start a fuel device, and raise the fuel pressure as quickly as possible by the driving of the electric fuel pump. However, for the fuel pressure to reach a predetermined value, a delay of predetermined period of time occurs in proportion to a piping capacity of the injector and the fuel pump. When the injector is driven during the delay, an injection amount is insufficient because the fuel pressure is insufficient. Therefore, it is necessary to prohibit the driving of the injector until the fuel pressure reaches the predetermined value. This causes a delay in the start of the engine.
Time required for raising the fuel pressure depends upon initial fuel pressure in pipes of the injector and the electric fuel pump before the start of the engine. In the case where rest time after the engine stop is long, the initial fuel pressure when the engine is started is lower in comparison with the case where the engine start and stop are repeatedly performed. Therefore, longer period of time is required until the fuel pressure reaches a predetermined pressure. In order to secure stable startability, it is necessary to set injector driving prohibition time according to this long period of time.
When the engine operation is continuously performed with high load and, after the operation, the engine is stopped and rested for several minutes, engine atmosphere temperature rises because of engine temperature. Therefore, in some case, the fuel temperature in the injector pipe rises and vapor (vaporization of the fuel) occurs. When the engine is started in a state in which the vapor occurs, in some case, the vapor is discharged from the injector even if the injector is driven, and hence a target amount of the fuel cannot be supplied to the engine and the engine cannot be started because of fuel insufficiency. In such a state, the manual start operation has to be repeated until the vapor is discharged from the injector or the engine has to be rested for a period of time enough for the engine to be sufficiently cooled and the vapor to be naturally eliminated.